Mitosis and Meiosis

What is Genetics?

the study of heredity and the variation of inherited characteristics through DNA

Chromosome

• tightly coiled packages of DNA found in the nucleus during mitosis

• Humans have 46 chromosomes (23 pairs).

Chromatin

the tangled fibrous complex of DNA found in the nucleus during interphase

Genes

• specific DNA sequence that contains a set of instructions for a specific trait

  • e.g. gene for eye colour, gene for ear shape

• humans have approximately 30 000 genes

Allele

• one of two or more forms of a gene

  • allele for blue eye colour or allele for brown eye colour

Karyotype

a picture of all the chromosomes of a cell arranged in homologous pairs

Homologous Pairs

• Chromosomes that carry the same genes but possibly different alleles; one homologue comes from mom and one comes from dad

• Arranged according to length, centromere location and banding pattern

Two Types of chromosomes

• Autosome - Chromosome that is not involved in determining the sex of an organism (In humans, pairs 1 - 22 are autosomes)

• Sex Chromosome - An X or Y chromosome, which determines the genetic sex of an organism

Cell Division and Chromosomes

• When new cells are required in the body, chromosomes must be duplicated to ensure each new cells receives a complete set of instructions

• Each chromatid contains a complete set of genetic information

DNA

• Deoxyribonucleic Acid

• Polymer

• The individual units (monomers) of DNA are called nucleotide
  A nucleotide is made up of 3 parts:

  1. pentose sugar (deoxyribose) 

  2.  nitrogenous base:

  • adenine (A)

  • guanine (G)

  • cytosine (C)

  • thymine (T)

3.  phosphate

purines

Adenine and guanine are double ring structures

pyrimidines

Thymine, uracil, and cytosine are single ring structures

DNA Shape/Structure

• DNA is a double helix (looks like a twisted ladder)

• Two strands of DNA bond together through “complementary base pairing”, dependent on:

  • Base size (purine-pyrimidine)

  • Number of hydrogen bonds